The present invention relates generally to aircraft gas turbine engines, and, more specifically, to a high bypass turbofan engine having a fan thrust reverser.
Turbofan gas turbine engines are commonly used for powering aircraft in flight. The turbofan engine includes a core engine surrounded by a core cowl, and is configured for powering a fan disposed upstream therefrom. A nacelle surrounds the fan and the forward portion of the core engine and is spaced therefrom to define an annular fan or bypass duct. The nacelle has a fan inlet at a forward end and a fan outlet or nozzle at an aft end defined around the core cowl.
A fan thrust reverser is commonly disposed in the aft section of the fan nacelle and is used for reversing thrust upon landing of the aircraft to enhance its stopping capability. The fan thrust reverser is typically mounted between an axially translatable aft cowl portion of the nacelle and a stationary forward cowl portion thereof.
A plurality of thrust reversing deflector doors are typically mounted around the inner perimeter of the aft cowl and are deployed to block the fan duct as the aft cowl is deployed aft. Suitable linear actuators are used to translate the aft cowl between its stowed or retracted position and its deployed or extended position which uncovers a substantially annular outlet for reversing thrust.
The thrust reverser outlet is defined between the forward and aft cowls and typically includes therein a conventional cascade of turning vanes. The cascade vanes are arranged in axial rows and are circumferentially divided into a multitude of cells or small passages through which the fan air is directed radially outwardly by the deflector doors during thrust reversal operation.
Since the nominal direction of the fan air channelled through the fan duct is axially aft, the cascade turning vanes are configured with an upstream directed inclination for turning and reversing the direction of the fan air as it is discharged through the reverser outlet during thrust reverse operation.
The cascade vanes may be straight or arcuate in axial section with constant area flow passages defined therebetween. Since the cascade vanes define a multitude of the flow passages or cells in the reverser outlet, the vanes themselves inherently occupy area in the reverser outlet and decrease the effective flow area thereof.
Accordingly, the reverser outlet must be correspondingly sized larger in area to offset the loss of area introduced by the cascade vanes themselves. This in turn requires an increase in the axial throw or translation aft of the aft cowl during thrust reverse operation. And, the overall weight of the nacelle is correspondingly increased by the introduction of the cascade turning vanes, by the additional nacelle length required for reverser throw, and by the associated components required for actuation thereof.
Furthermore, the aerodynamic efficiency of the cascade turning vanes themselves is inherently limited by their slatted configuration and multitude of cells, yet is typically acceptable due to the limited use of the thrust reverser for landing operation only.
Accordingly, it is desired to provide an improved thrust reverser having increased efficiency, and decreased weight and complexity for improving overall operation of the turbofan engine.
A thrust reverser includes axially adjoining forward and aft cowls defining a fan nacelle for surrounding a fan and core engine with a fan duct therebetween. The aft cowl has a forward face and the forward cowl has an aft face adjoining each other to define a reverser nozzle which converges radially outwardly. The aft cowl is translatable between a stowed position in which the reverser nozzle is closed and a deployed position in which the reverser nozzle is open for discharging fan air in a forward direction for thrust reversal.